Add NEWS item about mpool_base_disable_sbrk MCA param

This commit was SVN r14171.

NEWS

@@ -50,6 +50,8 @@ Trunk (not on release branches yet)
 1.2.1
 -----
 
+- Fix functionality allowing users to disable sbrk() (the
+  mpool_base_disable_sbrk MCA parameter) on platforms that support it.
 - Fixed a segfault if there was a failure opening a BTL MX endpoint.
 - Fixed a problem with mpirun's --nolocal option introduced in 1.2.
 - Re-enabled MPI_COMM_SPAWN_MULTIPLE from singletons.